Calcium is one of constituent ingredients of bones and teeth, and it is of importance as a factor regulating muscles, nervous systems and hormone secretion for maintaining functions of a living body. Furthermore it has been proved that it affects immunological functions. Though it is known that lack of calcium ingestion affects development of bone diseases, as well as adult diseases such as hypertension, ischemic heart diseases and endocrine diseases and calcium has been becoming of general interest, the amount thereof ingested in the food life is not yet sufficient in our country. Therefore, various calcium preparations and health foods containing calcium have been proposed and sold on the market for making up the deficiency.
For example, chemically synthesized calcium compounds, calcium compounds originating in shellfishes, crustaceans, eggshells and animals' bones, and calcium originating in plants such as seaweeds have been used so far, but the absorption in vivo of such calcium is not so high and in many cases where they are used as preparations or food additives, they have difficulties in their taste and flavor, so that they have not yet been in popular use.
The present inventor et. al have noted on obtaining calcium having good absorbability in vivo and nice taste and flavor upon ingestion, and capable of providing calcium preparations or food additives containing such calcium from natural animal materials which are stable calcium sources and, as a result of experiment and investigation, have found that calcium compounds obtained by baking external skeletons of sea urchins which are composed of spines and shells can satisfy such purpose, and have further proceeded with the investigation and development of a practical process for producing them, and of the formulation of a composition obtained through the process which contain, calcium compounds originating in sea urchins as a main component.
During such process, the inventor has discovered that the amount of calcium absorbed in vivo is remarkably increased by compounding an appropriate amount of chondroitin sulfate, which belongs to sulfomucopolysaccharides, into the thus obtained calcium compound, the result of which has been filed as Japanese Patent Application Hei 6-260996. As a result of further investigation and development, it has been found that addition of chondroitin sulfate markedly promotes the absorption of calcium in vivo not only in the case of calcium originating in shells of sea urchin but also in the case of calcium originating in other animals or ordinary calcium salts obtained by synthesis such as calcium lactate and calcium carbonate. As described above, absorption of calcium in vivo is promoted by the addition of chondroitin sulfate and it has been also found that the absorption shows specific dependence on the concentration of chondroitin sulfate.
Although the chondroitin sulfate markedly promotes the absorption of calcium in vivo, it is never likely that this increases calcium concentration in blood so rapidly as to break the calcium balance in blood.